Viewing opportunity in early morning darkness

November 29, 2011

Many of us have the opportunity to leave for work before sunrise in December and January, and it's worth pausing to view the objects that will move into the evening sky through the winter.

Earth's orbital motion shifts our "night window," the view opposite the sun, by about one degree each day. This means that each star you see at a given time one night will be about one degree to the west the next night. Since Earth rotates 1 degree in four minutes (360 degrees in 24 hours, or 15 degrees every hour), each star rises and sets four minutes earlier each night. Objects rising at 10 p.m. today will rise at 8 p.m. in a month (30 days times four minutes per day equals 120 minutes).

So give yourself a few minutes while scraping the car to watch Mars and Saturn as they move toward their retrograde motion and oppositions in March and April.

Article Photos

The figure shows the view to the southeast from the APO building site at Little Wolf Pond in Tupper Lake Wednesday morning at 5:30. The Big Dipper has risen high from its evening position on the northeast horizon. Arcturus (Arc-TOUR-us), second brightest star in the northern sky, can be located by following the arc of the Big Dipper's handle. Continuing that line, the "spike to Spica," locates both Spica (SPIKEuh) and Saturn, with Saturn brighter than Spica and closer to Arcturus.

Currently, Saturn is almost a billion miles from Earth but will close to 800 million miles and brighten to rival Arcturus at opposition when it rises at sunset on April 15. Because it is so distant, its retrograde loop is much smaller than Jupiter's or Mars'. Right now it is moving eastward, away from Spica. On Feb. 8, it will stop and begin its retrograde loop. On May 30, it will cross the line between Spica and Heze (HAY-zay) as it slows. On June 26 Saturn will stop in our sky and resume its eastward, prograde, motion and be a bright beacon in the southern sky at sunset.

Mars, about half way between the horizon and zenith at dawn, equals Saturn in brightness even though it is almost 20 times smaller than the more distant world. At a quarter of a billion miles, it is much closer and will close to 63 million miles at its closest

approach, just after its opposition on March 3. In the meantime, Mars provides a bright guide to the constellation of Leo the Lion, the constellation that, to me, looks most like what it represents.

Like Saturn, Mars is currently in prograde motion and moving quite

quickly, almost half a degree each day. Observe its position with respect to Regulus (REGG-you-luss) and Chertan (CHUR-tun) and its motion will become apparent in just a few days. When I am able to discern this motion, I feel a bond with people through the millennia who saw it but, unlike me, could not understand it or explain it. In January, Mars' motion will slow as it stops on Jan. 25 to move back toward Regulus. It will make it back to the line between Regulus and Chertan by April 15, the day that Saturn is at opposition and procrastinators scramble to file extensions on their tax returns.

Due to their eastward motion, these planets will remain visible through the evenings of summer with Mars passing within half a degree of the Autumnal Equinox on July second and catching up to Saturn in mid-August. They will dim, however as Earth's faster orbit leaves them on the far side of the sun. Saturn and then Mars will finally be lost to the glare of dusk in September and October.

Through the winter, however, Mars provides an excuse and a guide to the sky encircled by the Big Dipper, Bootes (Bo-OAT-ease, the Herdsman, with the o's pronounced as in cooperate), Virgo and Leo. The two bright stars of Canes Venatici, (KAY-nuss Ven-AT-iss-see, the Hunting Dogs) lie about half way between the handle of the Big Dipper and Coma Berenices (KO-ma, Bear-EN-i-seas, the Hair of Bernice).

This is the only constellation that honors a person who actually lived. Bernice was the daughter of the King of Cyrene and, as the wife of Ptolemy III, was Queen of Egypt from 266 to 221 BCE. Legend has it that she cut off her hair as an offering to Aphrodite for her husband's safe return from the Third Syrian War. It was taken to the heavens and placed very near to the north pole of our galaxy. As is the case near the south galactic pole, there are few bright stars as we look out of the galactic disk.

However, the fuzzy blur of Bernice's hair is actually a cluster of about 40 sibling stars. It's faint enough to easily be washed out by light pollution, but worth exploring with binoculars in a dark sky. Ancient Arabic lore had this cluster as a pond where a gazelle was startled by a twitch of the lion's tail and left wet hoof prints the Three Leaps of the Gazelle as she bolted. These carry the names of Alula (uh-LOO-luh) Borealis and Australis for the first leap (the northern star is the higher of each pair in the diagram), Tania (TAH-nih-yuh) Borealis and Australis for the second leap and Talitha (TAH-lith-uh) for the northernmost star of the third leap. The southern star of the third pair is simply known as Kappa Ursae Majoris.

From these, cast your eye and your binoculars rightward of the far side of Leo, to the Beehive star cluster in Cancer. Also known as the Praesepe (PRAY-suh-pee), this cluster is twice as far away as Coma and much richer, with around a thousand stars. It, too, is worthy of exploration with binoculars and, in fact, was one of the first objects studied by Galileo with his telescope!

Even if you don't have to be out of the house early in the morning, venture outside before dawn to note the progress of planets and star clusters that presented deep mysteries to the ancients. Though no longer mysteries, they remain objects of beauty and wonder to those who take time to know them.

If you have any questions about astronomy, please visit the Adirondack Public Observatory web site at apobservatory.org or email Aileen at aodonoghue@stlawu.edu.